Investigations of aortic strips in vitro will characterize 42 K turnover, active sodium transport and tension development of the hibernator. Cardiac output will be determined by means of an implanted flow probe, and peripheral resistance prior to and during hibernation will be estimated from measurements of flow and pressure. Variation of the plasma concentrations of urea, glucose and electrolytes throughout a hibernating cycle will be determined, as well as the excretion rates of these materials.